The present invention relates to membrane electrode cells and systems used in electrodeposition coating. More particularly, in certain embodiments, the present invention relates to advantageous membrane electrode cell assemblies having electrode enclosures wherein the membrane seal of the enclosure is provided by a compression-independent, bonded arrangement.
As further background, electrodeposition coating, or “electrocoating”, is broadly classified into two categories. Anionic electrodeposition uses anionic paints; cationic electrodeposition uses cationic paints. Both of these processes are in current commercial use.
Membrane electrode cells are commonly used in electrodeposition systems. Such cells act as opposing electrodes in the electrodeposition process, with the object being painted serving as the counter-electrode. Membrane electrode cells also serve in many systems to remove ions from the paint bath to maintain proper paint bath chemistry.
The membrane electrode cell can have many shapes, and often is shaped as a flat rectangle, arcuate or semi-circle, tube or cylinder. Electrodeposition processes employing such membrane electrode cells are disclosed for example in U.S. Pat. Nos. 4,851,102, 4,711,709 and 4,834,861.
The membrane used in a membrane electrode cell can be either ion-exchange or neutral. The membrane is arranged in such a fashion as to separate the electrocoating paint bath from the electrode. An electrolyte fluid flows between the inside of the membrane and the outside of the electrode. This electrolyte fluid, which is often comprised mostly of deionized water and a small amount of acid or amine (depending on the type of electrocoating employed), is responsible for flushing the ions that pass through the membrane into the membrane electrode cell from the paint bath. The conductivity of this electrolyte fluid usually is maintained in the range of 500 to 2,000 microSiemens/cm (microMho/cm).
To separate the electrode from the paint bath, it is a common practice to provide a seal between the membrane and other structural member(s) of the electrode cell. These seals have in the past commonly been achieved by mechanical elements such as bolted flanges, which form a pressure-dependent seal between the flange, membrane, and an outer rim or periphery of an electrode housing. These seals can be difficult to maintain, and present complications in repair and replacement operations.
In light of this and other background in the field, there remain needs for membrane electrode assemblies of simplified design and which are more readily repaired, replaced and/or maintained. The present invention is addressed to these needs.